1. Field of the Invention
The present invention relates to an optical information recording medium capable of recording, reproducing and erasing.
2. Description of the Prior Art
There have heretofore been used as the optical information medium, a read-only type one which can only read out recorded information, a direct-read-after-write type one which forms bits on a recording film by laser beam radiation to permanently record information, and an erasable type one which can arbitrarily record, reproduce and erase information, each exhibiting the characteristics of its own, respectively.
As the erasable type medium, there have been known a photomagnetic type which takes advantage of photomagnetic effect and a phase transition type which performs recording and erasing by taking advantage of the transition between a crystalline phase and an amorphous phase.
Various materials have been proposed as the recording material of the phase transition type but none of them has fully fulfilled the requisitions for this type of recording material.
For example, Te and Te-based material suffer from the defects that they are low-melting point materials, have a low crystallization temperature, a small difference between the crystallization temperature and the melting point and a poor resistance to even slight moisture causing deterioration of the surface thereof. On the other hand, Au-Si-based, and AuAl.sub.2 -based materials are hard to transfer into the amorphous phase, and Pd-Si-based material have a relatively high melting point and involves a fear of increasing damage to the substrate. In addition, the above-mentioned compounds suffer the drawback of being expensive in practical application since Te, Au and Pd are all rare metals.
Moreover, Te and Te-based material are defective in that they are apt to spatter the material in the step of writing information owing to the higher vapor pressure, thus making themselves nonendurable to repeated use.